Field of the Invention
This invention relates to a self-regulated device for temperature-stabilization of at least one connection point and to a plug-in connector which makes use of the device.
A first application of the invention relates to a thermoelectric couple or thermocouple formed by two suitably chosen conductors joined together at one end by soldering or welding. This device constitutes a temperature sensor which is very frequently used for measuring or regulating temperatures within a range of approximately -200.degree. C. to over 1800.degree. C.
Depending on the temperature range to be controlled, the pair of conductors is selected for example as follows:
from approximately -150.degree. C. to 400.degree. C., copper and constantan (mean sensitivity of the thermocouple: 50 microvolts per degree centigrade); PA0 from -50.degree. C. to 1100.degree. C., chromel and alumel (sensitivity of 40 .mu.V/.degree.C.); PA0 from 100.degree. C. to 1500.degree. C., platinum and platinum alloyed with 10% rhodium (sensitivity of 10 .mu.V/.degree.C.); PA0 from 500.degree. C. to 1800.degree. C., tungsten and tungsten alloyed with 20% rhenium (sensitivity of 15 .mu.V/.degree.C.).
It is known that the electromotive force which appears at the open ends of the thermocouple depends on the difference in temperature between the joined ends or junction and the free ends of the two metals or alloys (these latter being maintained at the same temperature). This electromotive force therefore provides a measurement of the difference in temperature and not an absolute measurement of temperature. If V designates the voltage measured with a millivoltmeter and expresses the electromotive force existing between the points mentioned heretofore, and if E(T) designates the function which gives said electromotive force from a reference temperature T.sub.o, calibration of the thermocouple is in fact defined by the equation: EQU V=E(T-T.sub.o) (1)
In practice, the thermocouple junction is placed for example in a furnace in which it is desired to measure the temperature T whilst the free ends are either at the ambient temperature or within an enclosure in which the temperature T.sub.o is well defined by a mixture of water and ice within a heat-insulated vessel. Alternatively, the free ends can be placed in a Peltier-effect device or else in an enclosure which is temperature-stabilized by another change of phase, preferably at a temperature in the vicinity of the ambient or environmental value.
The irksome requirement of a temperature-stabilized enclosure can be avoided by interposing an electronic circuit between the junction and the free ends of the thermocouple so as to correct the value of the electromotive force given by equation (1) when T.sub.o varies. In this case the right side of the equation is written as follows: EQU E(T-T.sub.o)=E.sub.1 (T)-E.sub.o (T.sub.o) (2)
Equation (1) therefore becomes: EQU V=E.sub.1 (T)-E.sub.o (T.sub.o) (3)
whence EQU E.sub.1 (T)=V+E.sub.o (T.sub.o) (4)
This accordingly results in an electronic circuit which produces a voltage V.sub.o such that: EQU V.sub.o =E.sub.o (T.sub.o) (5)
Equation (4) then becomes: EQU E.sub.1 (T)=V+V.sub.o (6)
whence T is derived by utilizing the calibration curve.
It is therefore not possible to graduate E.sub.1 (T) directly in degrees centigrade since T.sub.o is not fixed; furthermore, the circuit which gives the characteristic defined by equation (5) imposed by the nature of the thermocouple is relatively complex, thus constituting a further disadvantage.